THIS message is for adults who always seem too busy to exercise. The mum who sits at work all week, then sits in the car delivering children to events on the weekend. The middle-aged man who drives to the local shop because he’s in a hurry and the walk makes him tired.

At this week’s IPC Journal Club, my GP colleague Rockley Boothroyd mentioned a brief vignette which inspired a simple literature search, which led to a profoundly useful conclusion.

The information we discovered is not new, but in my 25 years of medical reading, I have never heard it expressed as such an elegantly simple take-home message.

The message is this:

Every minute of exercise you do as an adult gains you seven minutes of life.

Or, to put it another way:

If you don’t have time in your life to exercise, you won’t have time in your life.

Let’s backtrack. Dr Boothroyd mentioned he had observed a woman asking her husband to walk up a hill to fetch their car while she waited down the bottom to be picked up. Nothing unusual about that. The woman had therefore saved herself about one minute of puffing her way up the hill.

But what had she really saved? The husband was doing her a favour, but which of them gained?

We know that people who exercise live longer than people who don’t. This remains true even when you rule out all other known influences and compare people who are otherwise identical in terms of age, smoking, obesity, etc.

In other words, if a sedentary person changes nothing else except taking up exercise, their life expectancy will increase. So far, not too surprising.

But how does this gain in life expectancy compare to starting a cholesterol or blood pressure medication? Or to losing 10kg of that body fat? Or to going on the latest fad diet, or taking multivitamins, or meditating, or getting regular medical check ups or screening for cancer or heart disease?

The answer is: exercise runs rings around the lot of them! In fact, regular exercise probably increases life expectancy more than nearly any other health intervention you can think of, except quitting smoking and perhaps avoiding a career as a rapper. I recommend the video 23 and 1/2 hours for a good summary of the evidence.

So the woman spent that minute of her life waiting at the bottom of the hill instead of using it for moderate exertion. Surely, we journal clubbers reasoned, we should be able to calculate how much ‘life’ that cost her?

When we doctors recommend 30 minutes of exercise five times a week, there is no reason to think that the first minute does any less good than the last minute — in fact, the law of diminishing returns would suggest that the first minute is actually the most valuable.

The new Australian exercise guidelines for adults have just doubled the recommendation to 60 minutes per day, but more health is gained going from no exercise to a little, than from a little to a lot.

Who dost thy seven-fold gifts impart? Prayer Book, 1662

SO how much extra life did the woman gift to her husband by suggesting he walk up the hill?

When we did the maths, we calculated it at seven minutes.

See our Inala Primary Care Journal Club (IPCJC) blog ‘Evidence’ for details. Briefly, if you do 15 minutes of moderate exercise per day for 40 years, on average you will live an extra three years. This boils down to about 220,000 minutes of exercise giving you 1.6 million minutes of extra life – a gain of about seven minutes of life for each minute of exercise.

Is it ground-breaking research? No. Is it anything more accurate than a rough ‘rule of thumb’? No – obviously the well runs dry at some point: otherwise exercising for three and a half hours a day would lead to immortality!

But could it be a useful message to spread far and wide among people who don’t take the time to do any exercise? Absolutely!